Channel 4 chief executive David Abraham has said it would not have broadcast controversial Frankie Boyle sketches if it thought they were racist, but admitted the comedian's joke about Katie Price's son was wrong.

"The jury agreed as [media regulator] Ofcom had already done earlier. The Daily Mirror disagreed but in an important outcome for comedians in this country, they lost the case."

However, Abraham admitted the broadcaster had crossed the line with a joke in Tramadol Nights, broadcast in December 2010, about Price's disabled son Harvey which was later heavily criticised by Ofcom. He had approved the joke ahead of transmission and defended Boyle during the media regulator's investigation last year.

On Thursday night, the Channel 4 chief executive described Boyles' comments about Price's son as a "darkly satirical joke directed at Jordan".

"Ofcom did not share our view and concluded that the joke appeared to directly target and mock the mental and physical disabilities of her eight-year-old son which was highly offensive to the audience," Abraham said.

"They concluded that the case involved an erroneous decision on a matter of editorial judgement on the channel's part which we accepted and for which we apologised."

Abraham said: "We have sought to learn from these experiences whilst also avoiding the danger of a creative 'chilling effect' through our building."

He added: "Occasional offence seems inevitable given the remit to test boundaries and when cultural tastes are always fluid. Channel 4's producers have often exposed the differences between generations in terms of what is and isn't acceptable at any point in time.

"It is perhaps likely that our culture of risk taking will also on occasion take us over the line. But I have also learned that even the appearance of doing so for its own sake does not sit comfortably with the spirit of our remit."

Abraham also said the future of investigative journalism was under threat at a time of straitened economic circumstances and increasing legal challenges.

He warned that the libel laws were "rather like a knife that can cut both ways – in defence of the truth and of the vulnerable as well as being open to misuse by the powerful".

"The current scandal around Jimmy Savile reminds us all of both the value and of the challenges surrounding investigative journalism," he said.

"There remains a very real risk that the appetite for these projects will continue to be challenged both economically and legally and that is why Channel 4 News, Dispatches and Unreported World remain such key parts of the Channel 4 schedule."

"Channel 4 is not opposed to 'no win no fee' in providing the necessary access to justice for claimants," said Abraham.

"But we object to claimant firms being entitled to recover grossly inflated uplifts that are often disproportionate to the risk they run in bringing a claim.

"Often these costs are used to place financial pressure on media defendants to settle and encourage some claimants to bring unmeritous claims since they are not at risk. They also discourage others from reporting the truth in the first place for fear of such lawsuits."

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